fibonacci_collatz.c

/* This program is licensed under the GNU GPLv2 or later */

#include <gmp.h>
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

int main(int argc, char * argv[])
{

mpz_t a, b, c;

mpz_init_set_ui(a,1); /*  a = 1  */
mpz_init_set_ui(b,1); /*  b = 1  */
mpz_init(c); /* initialize c */

for (int i=1; i <= 1000 ; ++i){  /* Calculate the 1000th fibonacci number and Collatz it */
    mpz_add(c,a,b); /* c = a + b */
    mpz_mul_ui(a,b,1); /* a = b */
    mpz_mul_ui(b,c,1); /* b = c */
}


    mpz_t p;
    unsigned long int odd_or_even; /* odd_or_even is a flag */

    mpz_init_set_ui(p,1); /* initialize p */

    mpz_out_str(stdout,10,c); /* output n in base 10 */
    printf("\n");

    while ( mpz_cmp_ui(c,1) != 0)
    {
    mpz_mod_ui(p,c,2); /* p = mod(c,2) */
    odd_or_even = mpz_get_ui( p ); /* odd_or_even is integer version of mpz_t p */

        if (odd_or_even == 1) /*if c is odd */
        {
            mpz_mul_ui(c,c,3); /* c = 3c */
            mpz_add_ui(c,c,1);  /* c = c+1 */
        }
        else /* if c is even */
        {
            mpz_cdiv_q_ui(c,c,2); /* c = c/2 */
        }

    mpz_out_str(stdout,10,c); /* output c in base 10 */
    printf("\n");
    }

    mpz_clear(c);
    mpz_clear(p);
    return 0;
}